Recent work with both avian and mammalian infants has demonstrated that the sequential onset of functioning of the various sensory systems during prenatal development can serve as an important source of perceptual organization during the perinatal period. For example, evidence derived from precocial avian embryos and hatchlings indicates that unusually early (prenatal) visual experience can alter the normal functioning of both the auditory and visual systems during the postnatal period. However, the processes and mechanisms underlying this dynamic nature of early perceptual organization and the specific intramodal and intermodal consequences of such premature visual experience has only begun to be explicitly studied. In this application, research is proposed that will further our understanding of how sensory systems and their respective stimulation histories influence one another during late prenatal and early postnatal development, in order to establish how usual (or abnormal) sensory experiences serve to maintain, facilitate, or interfere with the usual course of perinatal intersensory development. Related studies, utilizing precocial avian embryos and hatchlings, will employ an "early exposure" design to examine: (I) what experiential factors determine whether modified sensory stimulation facilitates or interferes with early intrasensory and intersensory development, (2) the nature of the relationship between amount, type, and modality of sensory stimulation during the perinatal period, (3) the roles of embryonic attention and behavioral arousal in the development of early perceptual organization, and (4) how transient or long-lasting are the effects of modified prenatal sensory stimulation for precocial infants. From a health perspective, this research will provide an important source of comparative data for work concerned with intersensory development in the human infant. Relatively little attention has been paid to the consequences of providing sensory experience earlier in development than when it would normally be available, despite the fact that prematurely born human infants are routinely exposed to patterned visual stimulation at a developmental age when they would not ordinarily encounter such visual experience.